Apparatus and method for 2-dimensional steered-beam nxm optical switch using single-axis mirror arrays

ABSTRACT

A beam steering module and switching system. The steering module is composed of a N×M array of single axis mirrors able to rotate about a particular axis (X-axis), a second N×M array of single axis mirrors able to rotate about an axis orthogonal to that of the first N×M array of mirrors (Y-axis), and a relay lens designed to image the first mirror array onto the second mirror array such that the beam angle may be controlled in both the X and Y-axis by adjusting the angle of the appropriate mirrors in the X and Y mirror arrays. Two steering modules may be combined to form a switching system. With two such steering modules, it is possible to completely determine, at the plane of the output fiber array, the position and angle of an optical beam emerging from any of the input fibers.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a related to the following copending U.S.provisional applications, all of which are herein incorporated byreference: “Two-Dimensional Gimbaled Scanning Actuator with VerticalElectrostatic Comb-Drive for Actuation and/or Sensing” of Behrang Behin,Michael J. Daneman, Meng-Hsiang Kiang, Kam-Yin Lau, and SatinderpallPannu, docket number ONX-105/PROV; and “Self-Aligned Comb-DriveActuators” of Behrang Behin and Satinderpall Pannu, docket numberONX-106/PROV; and “Multi-Layer, Self-Aligned Vertical Comb-DriveElectrostatic Actuators and Fabrication Methods” of Behrang Behin andSatinderpall Pannu, docket number ONX-107/PROV.

FIELD OF THE INVENTION

[0002] This invention relates generally to fiber optic communications.More particularly, the invention relates to optical switches for N×Narrays of fibers.

BACKGROUND ART

[0003] Modern fiber optical communications systems direct opticalsignals over multiple fibers. Such systems require optical switches todirect light beams from any given fiber in an input fiber array to anygiven fiber in an output array. One class of optical switches uses anapproach called beam steering. In beam steering, the light from thefiber is selectively deflected or steered by one or more movable opticalelement from the input fiber to the output fiber. Suitable opticalelements include microelectromechanical system (MEMS) mirrors. MEMSmirrors are usually actuated by magnetic interaction, electrostatic, orpiezoelectric interaction. Typically, two sets of moveable mirrors areused to steer the beam. Each fiber has a small “acceptance window”. Thefiber only efficiently couples light that is incident within a narrowrange of angles and positions. Although a single mirror will generallydirect the beam from an input fiber to the correct output fiber, twomirrors ensure that the light beam enters the output fiber at thecorrect angle. If the beam makes too large an angle with the axis of thefiber, light from the beam will not couple properly to the fiber, i.e.there will be high losses.

[0004] Optical switches using the steering-beam approach have beendemonstrated in two primary implementations. The first uses lineararrays of mirrors with a single angular degree of freedom. Combining twosuch mirror arrays as shown in FIG. 1 allows an implementation of an N×Noptical switch, where the number of input and output channels is equalto the number of mirrors in each array. The first array steers anoptical beam from an input fiber to the appropriate mirror on the secondarray, which then steers the beam into the corresponding output fiber.This implementation uses simple single-axis mirrors; however, it islimited in its scalability since the optical path between fibers becomesunreasonably large for large port counts (e.g. >32×32), increasing theloss of the switch

[0005] The second implementation depicted in FIG. 2 uses two sets of2-dimensional mirror arrays, each mirror having two angular degrees offreedom. The input and output fibers are each also arranged in a2-dimensional grid with the same dimension as the mirror arrays. Themirrors in the first mirror array steer the optical beams from thefibers onto the appropriate mirror in the second mirror array which thensteers the beam into the corresponding fiber. This approach isconsiderably more scalable, since, due to its 2-dimensional layout, thesize of the mirror and fiber arrays grows as the square root of thenumber of input/output ports, which is much slower than in the case of a1-dimensional grid. Therefore, switches with much larger port count(>2000×2000) are possible. However, this implementation requires themirrors to rotate about two different axes. Such mirrors areconsiderably more difficult to design, fabricate, and control.

[0006] There is a need, therefore, for a beam steering apparatus thatuses single axis optical elements to switch optical signals in an N×Nfiber array.

OBJECTS AND ADVANTAGES

[0007] Accordingly, it is a primary object of the present invention toprovide a beam steering system that uses single axis optical elements.It is a further object of the invention to provide a beam steeringsystem wherein ability to switch a particular path is independent of thecurrent configuration of the switch

SUMMARY

[0008] These objects and advantages are attained by a beam steeringmodule. The steering module generally comprises first and second N×Narrays of single axis mirrors. The mirrors in the first array rotateabout a particular axis (X-axis) while the mirrors in the second arrayrotate about an axis different from the first axis (Y-axis). Relayoptics disposed between the two arrays image the first mirror array ontothe second mirror array such that the beam angle may be controlled withrespect to both the X and Y-axes by adjusting the angle of theappropriate mirrors in the first and second mirror grids. The relayoptics preserve at an image plane an angle of emergence with respect toan object plane. The relay optics typically comprise a confocalarrangement of lenses.

[0009] Two steering modules may be combined to form a beam steeringsystem. With two modules, it is possible to completely determine, at theplane of the output fiber grid, the position and angle of an opticalbeam emerging from any of the input fibers.

[0010] Embodiments of the steering modules of the present invention maybe used to selectively couple light from an input fiber in an N×N inputfiber array to any output fiber in an N×N output fiber array.

BRIEF DESCRIPTION OF THE FIGURES

[0011]FIG. 1 depicts a one-dimensional beam steering apparatus accordingto the prior art;

[0012]FIG. 2 depicts an isometric view of a two-dimensional beamsteering apparatus according to the prior art;

[0013]FIG. 3 depicts an isometric view of a beam steering apparatusaccording to a first embodiment of the present invention; and

[0014] FIGS. 4 depicts an isometric view of a beam steering apparatusaccording to a second embodiment of the present invention;

DETAILED DESCRIPTION

[0015] Although the following detailed description contains manyspecifics for the purposes of illustration, anyone of ordinary skill inthe art will appreciate that many variations and alterations to thefollowing details are within the scope of the invention. Accordingly,the following preferred embodiment of the invention is set forth withoutany loss of generality to, and without imposing limitations upon, theclaimed invention.

[0016] The optical switch system according to embodiments of the presentinvention switches light from any of a set of input fibers into any of aset of output fibers in a non-blocking fashion (i.e. the ability toswitch a particular path is independent of the current configuration ofthe switch). The switching system is generally built from steeringmodules. FIG. 2 depicts a steering module according to a firstembodiment of the present invention. The steering module 100 generallycomprises two 2-dimensional mirror arrays 110, 130 and relay optics 120disposed along an optical path between the mirror arrays. The mirrorarrays 110, 130 each typically comprise N×M arrays of single axismirrors 112, 132. Generally N and M are integers greater than one. Inthe special case of square arrays, N=M.

[0017] In the present application, a single axis mirror refers to amoveable mirror configured to rotate about a single axis. Mirrors 112and 132 rotate about axes 114, 134 that are different. Typically,mirrors 112 and mirrors 132 rotate about axes 114, 134 that aresubstantially orthogonal to each other. For example, mirrors 112 areconfigured to rotate about axes 114, oriented in a substantiallyhorizontal plane. Mirrors 132 are configured to rotate about axis 134oriented in a substantially vertical plane.

[0018] An input light beam 101 from a input fiber in a given row andcolumn of an N×M input fiber array (not shown) impinges on a givenmirror 112 in array 110. Mirrors 112 and 132 deflect the light beam 101towards a fiber in an N×M output fiber array (not shown). Those skilledin the art will recognize that because the propagation of light isreversible, the role of input and output fibers may be reversed.

[0019] In an exemplary embodiment, relay optics 120 comprises a firstfocusing element 122 and a second focusing element 124 in a confocalconfiguration. For the purposes of this application the “focusingelement” encompasses optical elements capable of focusing light. Suchelements include refractive elements such as lenses, reflective elementssuch as mirrors, diffractive elements and micro-optical elements. Lensesinclude simple lenses and compound, i.e. multiple element lenses, gradedrefractive index (GRIN) lenses, ball lenses, and the like. Diffractiveelements include Fresnel lenses and the like. In a confocalconfiguration, focusing elements 122 and 124 are characterized by thesubstantially same focal length f and separated from each other by adistance substantially equal to 2 f. Furthermore, array 110 is located adistance f from focusing element 122 and array 130 is located a distancesubstantially equal to f away from focusing element 124.

[0020] Relay optics 120 image mirror array 110 onto mirror array 130.The angle of beam 101 may be controlled with respect to both axes 114and 134 by adjusting the angle of the appropriate mirrors in the arrays110 and 130. For example, beam 101 emerges from mirror array 110 at anangle φ with respect to the object plane of relay optics 120. The objectplane of relay optics 120 is typically located proximate mirror array110. The image plane of relay optics 120 is typically located proximatemirror array 130. Relay optics 120 are configured to ensure that beam101 impinges on the image plane of relay optics 120 at the same angle φ.In other words, light beam 101 enters and leaves relay optics 120 at thesame angle. Furthermore, parallel light entering relay optics 120 leavesas parallel light.

[0021] Steering module 100 may be used for beam steering in smallport-count switches or if loss is not critical. Alternatively, module100 may be used to switch beam 101 from input fibers in an N×M array toa grid or array of photodetectors. Mirrors in array 110 deflect lightbeam 101 to the row containing the desired output fiber or detector.Mirrors in array 130 deflect beam 101 to the desired column on that row.

[0022]FIG. 3 depicts a steered beam switching system 200 according to asecond embodiment of the invention. If port count becomes sufficientlyon module 100, large losses may occur due to light entering the fibersat two great an angle. To overcome this, the system 200 that utilizestwo modules of the type shown in FIG. 2 to ensure that beam 101 entersthe output fiber at the correct angle.

[0023] The system 200 generally comprises a first module 210 coupled toan N×M input fiber array 202 and a second module 220 coupled to anoutput fiber array 204. Modules 210 and 220 determine, at the plane ofoutput fiber array 204, the position and angle of an optical beamemerging from any of the input fibers in input fiber array 202. Modules210 and 220 have features in common with module 100 of FIG. 2. Module210 comprises single axis mirror arrays 212, 214 and relay optics 216.Mirrors in arrays 212 and 214 rotate about mutually orthogonal axes.Module 220 comprises single axis mirror arrays 222, 224 and relay optics226. Mirrors in arrays 222 and 224 rotate about mutually orthogonalaxes.

[0024] In the exemplary embodiment depicted in FIG. 3 mirrors in arrays214 and 222 rotate about substantially parallel axes. A light beam 201from a fiber 203 in input fiber array 202 couples to a correspondingmirror 213 in mirror array 212. Mirror 215 steers light beam 201 to amirror 215 in array 214. Relay optics 216 preserve the angle that lightbeam 201 makes at with respect to an image plane of relay optics 216.Mirror 215 deflects light beam 201 to a mirror 223 on array 222. Mirror223 steers light beam 201 to a mirror 225 in array 224. Relay optics 226preserve the angle that light beam 201 makes at with respect to an imageplane of relay optics 226. Mirror 225 deflects light beam 201 to acorresponding fiber 205 in output fiber array 204.

[0025] Those skilled in the art will recognize that by suitablemanipulation of mirrors 213, 215, 223, and 225 any fiber in input array202 may be coupled to any fiber in output array 204.

[0026] It will be clear to one skilled in the art that the aboveembodiment may be altered in many ways without departing from the scopeof the invention. For example, although in the above embodiments, themirrors are described as MEMS mirrors other mirrors such as bulk mirrorsor large-area deformable mirrors may be used. Accordingly, the scope ofthe invention should be determined by the following claims and theirlegal equivalents.

What is claimed is:
 1. A beam steering apparatus comprising: a) a firstN×M array of mirrors, wherein N and M are integers and each mirror inthe first array is configured to rotate about a first axis; b) a secondN×M array of mirrors, wherein each mirror in the second array isconfigured to rotate about a second axis; c) relay optics disposed alongan optical path between the first and second arrays configured to imagea light beam emerging from a mirror in the first array onto acorresponding mirror in the second array, wherein the relay opticspreserve at an image plane an angle of emergence with respect to anobject plane.
 2. The apparatus of claim 1, wherein the first axis issubstantially perpendicular to the second axis.
 3. The apparatus ofclaim 1 wherein the mirrors in the first array are configured to deflectlight from one or more optical fibers in an N×N array of input fibers.4. The apparatus of claim 1 wherein the mirrors in the first and secondarrays are microelectromechanical MEMS) mirrors.
 5. The apparatus ofclaim 1 wherein an angle of a mirror in the first array and an angle ofa mirror in the second array determines a position and angle of thelight beam at the image plane.
 6. The apparatus of claim 1 wherein therelay optics comprises: i) a first focusing element having a first focallength; ii) a second focusing element having a second focal length. 7.The apparatus of claim 6 wherein the first and second focal lengths aresubstantially the same.
 8. The apparatus of claim 7 wherein the firstand second focusing elements are separated from each other by a distanceof twice their common focal length.
 9. The apparatus of claim 7 whereinthe first focusing element is separated from the first mirror array by adistance substantially equal to the first focal length.
 10. Theapparatus of claim 7 wherein the second focusing element is separatedfrom the second mirror array by a distance substantially equal to thesecond focal length.
 11. A beam steering apparatus comprising: a) afirst beam steering module; and b) a second beam steering moduleoptically coupled to the first beam steering module; wherein each of thefirst and second beam steering modules includes: i) a first N×M array ofmirrors, wherein N and M are integers and each mirror in the first arrayis configured to rotate about a single first axis; ii) a second N×Marray of mirrors, wherein each mirror in the second array is configuredto rotate about a single second axis; iii) relay optics disposed alongan optical path between the first and second arrays configured to imagea light beam emerging from a mirror in the first array onto acorresponding mirror in the second array, wherein the relay opticspreserve at an image plane an angle of emergence with respect to anobject plane.
 12. The apparatus of claim 11, wherein the first andsecond modules are configured to control, at a plane of an output fibergrid, a position and angle of a light beam emerging from any input fiberin an N×M array.
 13. The apparatus of claim 11 wherein an angle of amirror in the first array and an angle of a mirror in the second arraydetermines a position and an angle of the light beam at the image plane.14. The apparatus of claim 11 wherein the first and second beam steeringmodules are configured to direct a beam from an input fiber in an N×Minput fiber array to an output fiber in an N×M output fiber array. 15.The apparatus of claim 11 wherein at least one of the input and outputfiber arrays is an array of collimated fibers.
 16. The apparatus ofclaim 11 wherein the mirrors in the first and second modules aremicroelectromechanical (MEMS) mirrors.
 17. A beam steering method,comprising: a) coupling a beam of light to a first mirror in a first N×Marray of mirrors, wherein N and M are integers and each mirror in thefirst array is configured to rotate about a first axis; b) deflectingthe beam from the first mirror to a second mirror in a second N×M arrayof mirrors, wherein each mirror in the second array is configured torotate about a second axis; c) imaging the light beam emerging from thefirst mirror at the second mirror, while preserving at an image plane anangle of emergence with respect to an object plane.
 18. The method ofclaim 17 further comprising: d) deflecting the beam from the secondmirror to a third in a third N×M array of mirrors, wherein each mirrorin the third array is configured to rotate about a third axissubstantially parallel to the second axis; e) deflecting the beam fromthe third mirror to a fourth in a fourth N×M array of mirrors, whereineach mirror in the fourth array is configured to rotate about a fourthaxis substantially perpendicular to the third axis; and f) imaging thelight beam emerging from the third mirror at the fourth mirror, whilepreserving at an image plane an angle of emergence with respect to anobject plane.
 19. The method of claim 17 further comprising deflectingthe light beam from the fourth mirror to a selected output fiber in anN×M array of output fibers..
 20. The method of claim 19 wherein angularpositions of the first and second mirrors determines which fiber in theoutput fiber array is the selected.
 21. The method of claim 17 whereinthe object plane is located proximate the first array.
 22. The method ofclaim 17 wherein the image plane is located proximate the second array.23. The method of claim 17 wherein the beam of light originates at aninput fiber in an N×M input fiber array.